The "closing" variable is used as boolean and set to "true" in one
place, update the declaration of that variable and their other
assignment to proper type.

Fixes: e951747a ("IB/uverbs: Rework the locking for cleaning up the ucontext")
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>